Signal translating apparatus



April 4, 1944- l.. JQ ANDERSON ETAL 2,345,996

SIGNAL TRANSLATING APPARATUS Filed Dec. '7, 1940 v #waff/cy Enventorgg las@ Jlderov fomeg PatentedI Apr. 4, 1944 2,345,998 SIGNAL TRANSLATING APPARATUS Leslie J. Anderson and Alfred H. Kettler, Haddon- Held,

N. J., signore to Radio Corporation of America, a corporation of` Delaware Alpilmion December 7, 1940, serial rc. :eases s claims This invention relates to signal translating apparatus, and more particularly to a sound-powered throat microphone to be worn on the users throat and actuated by theiarynx, the principal object of our invention being to provide an improved microphone oi this type which is very rugged in construction and which has high sensitivity.

More particularly, it is an object of our present invention to provide an improved throat microphone which has suificient sensitivity and intelligibilityto operate directly into 4sound-powered telephone receivers without the need of an amplifler.

It is also an object of our invention to provide an improved microphone as set forth above which is simple in construction, is comprised of a minimum number of parts, may be readily assembled and taken apart, and which is highly efficient in use.

In accordance with this invention, we provide a microphone consisting oi a casing in which are housed two diaphragms slightly spaced from each other to provide a volume of air therebetween, this volume of air constituting a fluid coupling between the two diaphragms. To one of the dlaphragms is secured an actuating button which extends through a suitable opening in the casing and which rests against the -wearers throat when the microphone is applied. The other diaphragm is coupled to the vibrating reed or armature of an electromechanical signal translating unit, preferably of the balanced armature type, by means of a driving rod or the like. 'Ihe air volume between the two diaphragms provides A.C. coupling therebetween without transmitting D.C. forces, such as are applied when the aforementioned button is pressed against the wearers throat, thus allowing the armature to remain properly balanced in the air gap of the translating device independently of the pressure against the wearers throat. One of the two diaphragms, preferably the second-named one, is provided with a small opening therein which affords communication between the air in the space between the two diaphragms and the air external to said space. This diaphragm opening and the volume of air between the two diaphragms are of such size that the mass of air in the opening resonates with the aforementioned volume of air preferably at 'the' lowest frequency it is desired not to be greatly attenuated. The diaphragm opening will cause the D.C. components due to pressure of the throat against the actuating button to be infinitely attenuated. It thus forms a simple and very effective acoustic filter in the system. The space between the two diaphragme is made such that the impedance of the air volume therein is large compared to that of the moving system constituted by the second diaregion, where resonance occurs. Thus.

phragm. the armature, and the connecting rod therebetween in the upper part of the spectrum it is desired to pick up (for example, in the neighborhood of 2G00 to 2500 cycles). Preferably, the vibrating system which includes the second diaphragm is stiffness-controlled up to the same frequency characteristic is obtained, which, in conjunction with the low frequency attenuation, gives intelligible speech when used without additional compensation. When used with soundpowered telephones of limited range in the lower region, the intelligibility of the system as a whole is greatly improved.

The novel features that we consider characteristic of our invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawing in which Figure 1 is a central sectional view of one form of microphone according to our invention,

Figure 2 is a sectional view taken approximately on the plane of line II-II of Figure l,

Figure 3 is a perspective view of the pole structure of the translating unit,

Figure 4 is a fragmentary sectional view of a slightly modified form of actuating button for the microphone,

Figure 5 is a set of response curves showing the response of our improved microphone,

Figure 6 is a wiring diagram showing the electrical analogy to the acoustical system of our imf proved microphone, and

Figure 6 is a view showing a neckband embodying, as a pair of operating units, two microphones formed according to our invention.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown. in Figure l, a casing comprised of upper and lower members i and 3, respectively, which may be threadedly united and the former of which is provided with an opening 5. Clamped within the casing between the portions I and 3 thereof are a pair of diaphragms l and 9 which are mounted for vibration in more or less conventional manner. To the upper diaphragm 1 is cemented or otherwise suitably secured a button I0 which extends through the opening 5 and which is adapted to be placed against the throat of the wearer when the unit is in operative position. If desired, a rubber seal 8 may be placed around the button I0 and against the casing part I. The second diaphragm 9 is connected, by means of a drive rod Il, to an armature Il clamped at one end between a pair of pole pieces II and I1, preferably having overlapping pole a rising4 laces, as clearly shown in Figure 8. so that the entire assembly maybe very shallow. The armau ture I3 operates in the air gap between the pole is supplied by a magnet I9, a coil Il surrounda ing the armature il,A and the armature le is norxnmly balanced so that it is disposed centrally between the .pole pieces ld and lll, .as clearly shown in lEigure l..

The diaphragm d is provided with one or more small openings il which will aiiord communie cation between the volume oi air in the space 23 between the diaphragme l and d and the air external to the space 23. A".lhe acoustical system described above is analogous to that shown in the electrical wiring diagram ol Figure d where mi is the mass oi the button l@ and the dia phragm l, ci is the compliance of the diaphdegm l,

laces of the pole pieces l5 and ll to which nur:

c2 is the compliance of the volume or air in the Ilwo units, such as that described above, may be assembled within the pockets 2S of a necs= band 2l which is placed around the wearers throat and suitably tightened so that the buttons lil will be irmly pressed against the larynx. Throat or larynx vibrations are picked up by the buttons ld and are transmitted to each oi the diaphragme l. Preferably, the buttons and their associated diaphragme should be as light as it is practical to make them and reasonably ringed. The motion of the diaphragme l is, in each case, transmitted to the diaphragme@ by means oi the volume of air in the spacm 25. The open= ing 2l in each of the diaphragmm is preier= ably of such size that the air mass therein res= onates with the volume oi air in the space 33 at the lowest frequency it is desired not to attenuate greatly. The openings al will cause the D.-C. components, due to the pressure oi' the throat against the buttons it, to be innitely attenuated. Hence, it forms a simple, though necessary, acoustic lter. Preferably, the air space 23 should be such that the impedance oi the air therein is large compared to the com binedy impedance of the diaphragm 9, the drive rod il, and the armature i3 up to apprturimateu ly 2000 to 2500 cycles. By making the vibratory system which includes the diaphragm 5 in each case stillness-controlled up to the same region, a rising frequency characteristic is obtained which, in conjunction with the .low irequency attenuation, will give intelligible speech without requiring additional compensation.

Figure 5 shows a set of curves indicating the response which may-be vobtained with., our im proved microphone. The curve A, representing the characteristic of the larynx, shows a peak in the 'lower region. The curve B, representing the response of our improved microphone, shows a peak in the ,upper region. The combination ofthe two is shown by the dotted line C. 'which represents the overall response oi the larynx and our improved microphone.

In Figure 4, there is shown a slightly modided arrangement wherein the buttoni0 is provided with anl annular shoulder 28 normally spaced from but adapted to engage the casini; part l. This may be important where, in some cases, it is desired to enable the button 6d to take great 'shocks without, however, transmita ting them to the diaphragm l.

Although we have shown and described but one microphone in accordance `with our inven-a tion, it will be apparent to those skilled in the artthat many modidcations thereof, as well as changes in the one described, are possible. Therefore, we dei not wish to limit ourselves except insoi'ar as is made necessary by the prior art and by the spirit o the appended claims.

We claim as our invention:

l. Athroat microphone adapted to be worn on the throat of theuser for actuation by the larynx, saidmicrophone comprising a casing, a pair of diaphragme vibrativeiy mounted within said casing in spaced relation to each other and conning a volume oi air'therebetween, said volunie oi air constituting a coupling between said diaphragme, actuating means coupled'to one oi said diaphragms and extending outwardly oi said casing for engagement with the tbnoat oi the wearer, an electromechanical translating device in said casing including an active element, and means coupling the second o said diaphragme to said element, 'said second diaphragm being pron vided with at least one opening therein aord= ing communication between said volume oi air and the air external thereto, said opening and said volume being of such size that the massV of air in said openingresonates with said air volume at substantially the lowest signal ire- V quency it is desired to have the microphone translate without substantial attenuation.

2. A throat microphone according to claim l characterized in that the impedance oi said volume or air is large compared with the impedance oi? the movable system comprised of said second diaphragm, said active element, and said coupling means therebetween within predetermined limits. v

3. A throat microphone according to claim l characterized in that the impedance oi said volume of air up to approximately between 2000v and 2500 cycles is large compared with the impedance of the movable system comprised of said second diaphragm, said active element, and said coupling means therebetween.

4. A throat microphone according to claim l characterized in that the vibratile system comprised of said second diaphragm, said active element and said coupling means therebetween is stillness-controlled.

5. A throat microphone according to claim li characterized in that said translating device is of the electromagnetic, balanced-armature type oi which the amature constitutes said active element.

LESLIE J. ANDERSON. ALFRED H. KE'I'lLm. 

